The present invention relates to a method and an apparatus for crushing and pulverizing used and waste tires for effective recycling and re-use of rubber materials by separating iron and steel components embedded in the tires such as piano wires and steel fibers.
Today, as many as about 100 million tires are turned to waste materials as waste or used tires each year in this country. The used tires are stacked high on open space in suburban areas, and these tires not only spoil and hurt the view of the city but may cause disaster by spontaneous ignition and fire. The recycling ratio of the waste tires exceeds now 90%, and this is the best among the industrial waste. As a matter of fact, however, this may not be true. When we investigate the real state of recycling of waste tires in detail, more than one half of the waste tires are burned and used for power generation or for firing of cement. This is, so to speak, a disposal by incineration.
The tires and technology on tires have been advancing on the way of evolution, being turned to composite materials of increasingly higher grade in association with the incessant progress of performance characteristics of automobile. FIG. 4 shows the details of inner portion of a radial tire, which is main stream of the tires used at present. Chemical fiber cords such as nylon, polyester, etc. are woven just like a bamboo blind, and by covering both surfaces with rubber, a carcass 25 is formed. This constitutes a skeleton for a tire. Both ends of the carcass 25 to be engaged with rim are wound up on a bead 26, which comprises a bundle of piano wires of about 1 mm in diameter. Between the carcass and a tread 27, i.e. a rubber layer to be in contact with road surface, a cloth-like steel belt 28 woven with very fine steel fibers is buried, and this fastens the carcass and reinforces it just like a hoop on a barrel. As described above, a tire comprises rubber, fibers such as steel, nylon, etc., and piano wires, and these components are integrated with the rubber as adhesive agent. This poses a great obstacle for recycling of the used tires. Above all, it is absolutely necessary to completely separate piano wires and steel fibers from rubber components in a process to produce rubber powder suitable for re-use. For this purpose, crushing, pulverizing, and magnetic separation must be repeatedly performed, and this requires facilities of very large scale.
The rubber powder obtained from waste tires is very useful. It can be used as paving material to prevent the freezing of road surface, and there are many other applications. At present, however, rubber powder is very expensive, being at a price of about 200 yen per kg in case of rectangular chips of about 5 mm in size, and this hinders the utilization for practical use. Apart from discussing whether it is lucky or unlucky, waste tire chips can be used as a fuel of high quality, and it is still firmly believed that the tire chips should be burned in any case. On the other hand, in Europe and America, tires are recycled for two or three times by re-attaching tread rubber. In our country where almost all of the materials are imported, mass consumption of rubber materials are still continued, and this situation should be avoided. We must positively attempt to turn away from thermal utilization of waste tires and must make efforts toward the material recycling by utilizing the excellent property of the rubber components.
At present, for the purpose of crushing and pulverizing tires, biaxial shearing type crushing and monoaxial impact type pulverizer are used. In both cases, biaxial rotary blades with sharp edges or rotary blades and fixed blades are used. The gap between the blade edges is decreased, normally to about 0.1 mm, and by relative movement of blade edges, tires are crushed and ruptured together with rubber, piano wires, and steel belt. In this process, it has been an important problem how long the sharpness of the blade edges can be maintained, or whether the blade can be easily replaced or not when blade edges are worn out. After passing through this process, the tires are crushed and pulverized to small pieces. There are usually iron components buried in the rubber components and these are often difficult to separate by means of magnet, and it is normally not possible to completely remove iron components when the crushed tires are passed through a magnetic separator only once. In this respect, magnetic separation process must be performed two or three times, while the tire chips are crushed and pulverized stepwise.